Small zooming lens, and digital camera and video camera both having same

ABSTRACT

A first lens group (G 1 ) fixed with respect to the image plane includes a lens ( 11 ) having a negative refractive power, a lens ( 12 ) having a positive refractive power and a lens ( 13 ) having a positive refractive power. A second lens group (G 2 ) has a negative refractive power as a whole, and causes a zooming action when moved along the optical axis. An aperture stop is fixed with respect to the image plane. A third lens group (G 3 ) includes a lens ( 31 ) having a negative refractive power and a lens ( 32 ) having a positive refractive power, has a positive or negative refractive power as a whole, and is fixed with respect to the direction of the optical axis when zooming and when focusing. A fourth lens group (G 4 ) has a positive refractive power as a whole, and moves along the optical axis such that the image plane, which is displaced by a movement of the second lens group (G 2 ) along the optical axis and by a movement of the object, is maintained at a constant position with respect to a reference plane. Thus, it is possible to realize a compact and high-image quality small zoom lens that is suitable for three-CCDs.

TECHNICAL FIELD

The present invention relates to small zoom lenses that can be usedsuitably for ultrasmall optical systems for three CCDs that acre usedfor video cameras and the like. The invention also relates to digitalcameras and video cameras using such small zoom lenses.

BACKGROUND ART

Conventionally, high-image quality optical systems for three CCDs havebeen proposed.

For example, the zoom lens disclosed in JP H6(1994)-347697A isconstituted by four lens groups having a positive, a negative, apositive and a positive refractive power, as viewed from the objectside, and performs zooming with the second lens group and focusing withthe fourth lens group. Further, the third lens group is constituted by asingle lens including an aspherical surface.

Similarly, the zoom lens disclosed in JP2000-305016A is constituted byfour lens groups having a positive, a negative, a positive and apositive refractive power, as viewed from the object side, and performszooming with the second lens group and focusing with the fourth lensgroup.

However, in order to ensure a back focus for inserting color separationprisms, and to shorten the focal length at the same time, it isnecessary to weaken the refractive power of the third lens group. Whenthe third lens group is constituted by a single lens as in JPH6(1994)-347697A, the curvatures of the lens surfaces are reduced withdecreasing refractive power, so that it is not possible to perform theaberration correction sufficiently. Or, the curvature of the surface onthe object side and that of the surface on the image side become closeextremely, thus making it difficult to perform processing such ascentering. In JP2000-305016A, the third lens group is constituted by twolenses, so that the processing limitations can be reduced. However, thefirst lens group is constituted by three single lenses and therefore isdifficult to be assembled, and the second lens group is constituted byfour single lenses, so that it is not possible to reduce the cost.

DISCLOSURE OF INVENTION

The present invention has been made in order to solve theabove-described problems, and it is an object of the invention toprovide a compact, high-image quality small zoom lens that is suitablefor three CCDs.

In order to achieve the above-described object, a small zoom lensaccording to the present invention is provided with a first lens groupthat includes a lens having a negative refractive power, a lens having apositive refractive power and a lens having a positive refractive power,arranged in that order from an object side, that has a positiverefractive power as a whole, and that is fixed with respect to an imageplane; a second lens group that has a negative refractive power as awhole, and that causes a zooming action when moved along an opticalaxis; an aperture stop that is fixed with respect to the image plane; athird lens group that includes a lens having a positive refractive powerand a lens having a negative refractive power, that has a positive ornegative refractive power as a whole, and that is fixed with respect toa direction of the optical axis when zooming and when focusing; and afourth lens group that has a positive refractive power as a whole, andthat moves along the optical axis such that the image plane, which isdisplaced by a movement of the second lens group along the optical axisand by a movement of the object, is maintained at a constant positionwith respect to a reference plane.

Furthermore, a digital camera and a video camera according to thepresent invention each include the above-described small zoom lens ofthe present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the configuration of a small zoom lensaccording to Embodiment 1 of the present invention.

FIGS. 2A to 2E are aberration charts for a small zoom lens according toWorking Example 1 of the present invention at the wide-angle end.

FIGS. 3A to 3E are aberration charts for the small zoom lens accordingto Working Example 1 of the present invention at the standard position.

FIGS. 4A to 4E are aberration charts for the small zoom lens accordingto Working Example 1 of the present invention at the telephoto end.

FIGS. 5A to 5E are aberration charts for a small zoom lens according toWorking Example 2 of the present invention at the wide-angle end.

FIGS. 6A to 6E are aberration charts for the small zoom lens accordingto Working Example 2 of the present invention at the standard position.

FIGS. 7A to 7E are aberration charts for the small zoom lens accordingto Working Example 2 of the present invention at the telephoto end.

FIGS. 8A to 8E are aberration charts for a small zoom lens according toWorking Example 3 of the present invention at the wide-angle end.

FIG. 9A to 9E are aberration charts for the small zoom lens according toWorking Example 3 of the present invention at the standard position.

FIG. 10A to 10E are aberration charts for the small zoom lens accordingto Working Example 3 of the present invention at the telephoto end.

FIG. 11 is a diagram showing the configuration of a small zoom lensaccording to Embodiment 2 of the present invention.

FIGS. 12A to 12E are aberration charts for a small zoom lens accordingto Working Example 4 of the present invention at the wide-angle end.

FIGS. 13A to 13E are aberration charts for the small zoom lens accordingto Working Example 4 of the present invention at the standard position.

FIGS. 14A to 14E are aberration charts for the small zoom lens accordingto Working Example 4 of the present invention at the telephoto end.

FIGS. 15A to 15E are aberration charts for a small zoom lens accordingto Working Example 5 of the present invention at the wide-angle end.

FIGS. 16A to 16E are aberration charts for the small zoom lens accordingto Working Example 5 of the present invention at the standard position.

FIGS. 17A to 17E are aberration charts for the small zoom lens accordingto Working Example 5 of the present invention at the telephoto end.

FIGS. 18A to 18E are aberration charts for a small zoom lens accordingto Working Example 6 of the present invention at the wide-angle end.

FIGS. 19A to 19E are aberration charts for the small zoom lens accordingto Working Example 6 of the present invention at the standard position.

FIGS. 20A to 20E are aberration charts for the small zoom lens accordingto Working Example 6 of the present invention at the telephoto end.

FIG. 21 is a diagram schematically showing the configuration of a videocamera according to Embodiment 3 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A zoom lens according to the present invention is provided with a firstlens group, a second lens group, an aperture stop, a third lens groupand a fourth lens group, arranged in that order from an object side.

The first lens group includes a lens having a negative refractive power,a lens having a positive refractive power and a lens having a positiverefractive power, arranged in that order from the object side, has apositive refractive power as a whole, and is fixed with respect to theimage plane.

The second lens group has a negative refractive power as a whole, andcauses a zooming action when moved along the optical axis.

The aperture stop is fixed with respect to the image plane.

The third lens group includes a lens having a positive refractive powerand a lens having a negative refractive power, has a positive ornegative refractive power as a whole, and is fixed with respect to thedirection of the optical axis when zooming and when focusing.

The fourth lens group has a positive refractive power as a whole, andmoves along the optical axis such that the image plane, which isdisplaced by a movement of the second lens group along the optical axisand by a movement of the object, is maintained at a constant positionwith respect to a reference plane.

With the above-described configuration, it is possible to realize ahigh-image quality small zoom lens that can be used suitably for threeCCDs.

In the above-described zoom lens of the present invention, it ispreferable that the second lens group includes at least one asphericalsurface, and includes a meniscus negative lens whose convex surfacefaces the object side, a lens having a negative refractive power and alens having a positive refractive power, arranged in that order from theobject side.

With this preferable configuration of the second lens group, it ispossible to reduce the flare due to off-axis lower rays by theaspherical surface, while suppressing the chromatic aberration whenzooming.

Furthermore, in the above-described small zoom lens of the presentinvention, it is preferable that the third lens group includes at leastone aspherical surface, and includes a meniscus negative lens whoseconcave surface faces the object side and a lens having a positiverefractive power, arranged in that order from the object side.

By disposing a lens having a positive refractive power on the imageplane side in the third lens group in this manner, the height of thelight rays incident on the fourth lens group is decreased, thus reducingthe diameter and weight of the lens. Accordingly, it is possible toreduce the power consumption required for the actuator when focusing.

Further, in the above-described small zoom lens of the presentinvention, it is preferable that the third lens group satisfies thefollowing Condition (1):4.01<|f3/f4|<60, where  (1)

f3: focal length of the third lens group,

f4: focal length of the fourth lens group.

Condition (1) is an expression relating to the focal length ratio of thethird lens group and the fourth lens group. If the lower limit isexceeded, then the refractive power of the fourth lens group becomes tooweak, so that the amount of movement of the lens when focusingincreases. If the upper limit is exceeded, then the refractive power ofthe fourth lens group becomes too strong, so that the fluctuation ofaberration due to focusing increases.

Furthermore, in the above-described small zoom lens of the presentinvention, it is preferable that the third lens group satisfies thefollowing Condition (2):14<|f3/fw|<210, where  (2)

f3: focal length of the third lens group,

fw: focal length of the entire system at the wide-angle end.

If the lower limit of Condition (2) is exceeded, then the refractivepower of the third lens group becomes too strong, so that the sphericalaberration is generated. If the upper limit is exceeded, then therefractive power of the third lens group becomes too weak, so that it isdifficult to correct the field curvature.

Further, in the above-described small zoom lens of the presentinvention, it is preferable that the third lens group satisfies thefollowing Condition (3):3<|f3/BFw|<55, where  (3)

f3: focal length of the third lens group,

BFw: back focus at the wide-angle end.

If the lower limit of Condition (3) is exceeded, then it is difficult tosecure an air space sufficient to insert color separation prisms. If theupper limit is exceeded, the back focus becomes too long, so that it isdifficult to achieve compactness.

Further, in the above-described small zoom lens of the presentinvention, it is preferable that the third lens group satisfies thefollowing Condition (4):0.85<|f31/f32|<1.5, where  (4)

f31: focal length of the first lens from the object side of the thirdlens group,

f32: focal length of the second lens from the object side of the thirdlens group.

If the lower limit of Condition (4) is exceeded, then the negativerefractive power becomes too strong, so that the negative Petzval Sumincreases. Moreover, the diameter of the lens disposed on the image sidebecome too large, which is unfavorable for achieving compactness. On theother hand, if the upper limit is exceeded, then the positive refractivepower becomes too strong, so that the spherical aberration and the axialchromatic aberration cannot be corrected sufficiently.

Furthermore, in the above-described small zoom lens of the presentinvention, it is preferable that the third lens group satisfies thefollowing Conditions (5) and (6):|nd31−nd32|<0.15  (5)|vd31−vd32|<3.0, where  (6)

nd31: refractive index of the lens of the third lens group that is onthe object side,

nd32: refractive index of the lens of the third lens group that is onthe image side,

vd31: Abbe number of the lens of the third lens group that is on theobject side,

vd32: Abbe number of the lens of the third lens group that is on theimage side.

In the case of the third lens group, the height of axial rays is largestwhen at the wide angle. If the upper limit of Condition (5) is exceeded,then the refractive index difference between the lens on the object sideand the lens on the image side becomes too large, so that the burden onone of the lenses increases; accordingly, higher order sphericalaberration, in particular, tends to be generated. If the upper limit ofCondition (6) is exceeded, then the axial chromatic aberrationincreases.

Furthermore, in the above-described small zoom lens of the presentinvention, it is preferable that the fourth lens group includes at leastone aspherical surface and a pair of cemented lenses, and includes alens having a positive refractive power, a lens having a negativerefractive power and a lens having a positive refractive power, arrangedin that order from the object side.

With this preferable configuration of the fourth lens group, it ispossible to reduce the height of light rays incident on the negativelens, which is favorable in terms of the Petzval Sum. Moreover, sincethe final lens is a lens having a positive refractive power, it ispossible to reduce the angle of incidence of the off-axis rays on CCDs.

Furthermore, it is preferable that when a refractive power of thesurface of the fourth lens group that is closest to the object side is φ41 and the maximum image height is RIH, the following Condition (7) issatisfied:0.005<φ41/RIH<0.035  (7)

If the upper limit of Condition (7) is exceeded, then the refractivepower becomes too strong, so that the spherical aberration and the comaaberration increase. If the lower limit is exceeded, then it is notpossible to obtain a refractive power sufficient to correct theaberrations, so that the spherical aberration and the coma aberrationcannot be corrected sufficiently.

Further, it is preferable that a single lens is disposed closest to theobject side in the fourth lens group, and when a refractive power of thesurface of the single lens that is on the object side is φ 41 and arefractive power of the surface of the single lens that is on the imageside is φ42, the following Condition (8) is satisfied:0.04<(φ41−φ42)/RIH<0.06  (8)

Alternatively, it is preferable that the fourth lens group includes acemented lens constituted by a lens having a positive refractive powerand a lens having a negative refractive power, and a single lens havinga positive refractive power, arranged in that order from the objectside, and when a refractive power of the surface of the cemented lensthat is closest to the object side is φ41 and a refractive power of thesurface of the cemented lens that is closest to the image side is ∥43,the following Condition (9) is satisfied:0.025<(φ41−φ43)/RIH<0.045  (9)

If the upper limits of Condition (8) and Condition (9) are exceeded,then the amount of aberration to be corrected by a single group becomestoo large, so that the performance deterioration becomes significantwhen lens eccentricity occurs. If the lower limits are exceeded, thenthe aberration correction in a state where there is no eccentricity isnot performed sufficiently, although the performance deterioration dueto eccentricity is reduced.

Furthermore, according to a video camera and a digital camera of thepresent invention, a video camera and a digital camera that are compactand exhibit high performance can be provided by using the zoom lens ofthe present invention.

Hereinafter, embodiments of the zoom lens according to the presentinvention will be described in detail with reference to the accompanyingdrawings and tables.

EMBODIMENT 1

FIG. 1 shows the configuration of a small zoom lens according toEmbodiment 1 of the present invention.

The small zoom lens according to this embodiment is provided with afirst lens group G1, a second lens group G2, an aperture stop (notshown), a third lens group G3 and a fourth lens group G4, arranged inthat order from the object side.

The first lens group G1 includes a lens 11 having a negative refractivepower, a lens 12 having a positive refractive power and a lens 13 havinga positive refractive power, arranged in that order from the objectside, has a positive refractive power as a whole, and is fixed withrespect to the image plane.

The second lens group G2 has a negative refractive power as a whole, andcauses a zooming action when moved along the optical axis. The secondlens group G2 includes at least one aspherical surface, and includes ameniscus negative lens 21 whose convex surface faces the object side, alens 22 having a negative refractive power and a lens 23 having apositive refractive power, arranged in that order from the object side.

The aperture stop is fixed with respect to the image plane.

The third lens group G3 has a positive or negative refractive power as awhole, and is fixed with respect to the direction of the optical axiswhen zooming and when focusing. The third lens group G3 includes atleast one aspherical surface, and includes a meniscus negative lens 31whose concave surface faces the object side and a lens 32 having apositive refractive power, arranged in that order from the object side.

The fourth lens group G4 has a positive refractive power as a whole, andmoves along the optical axis such that the image plane, which isdisplaced by a movement of the second lens group G2 along the opticalaxis and by a movement of the object, is maintained at a constantposition with respect to a reference plane. The fourth lens group G4includes at least one aspherical surface, and includes a lens 41 havinga positive refractive power, a lens 42 having a negative refractivepower and a lens 43 having a positive refractive power, arranged in thatorder from the object side. The lens 41 and the lens 42 that are on theobject side constitute a cemented lens, and the lens 43 on the imageside is a single lens.

In FIG. 1, reference numeral 212 denotes a cover glass, a low-passfilter, an IR cut filter and the like in a simplified manner, and 213denotes color separation prisms in a simplified manner.

In FIG. 1, ri (i is a positive integer) represents the curvature radiusof the i-th lens surface, counting from the object side, and di (i is apositive integer) represents the i-th lens thickness or air spacebetween lenses, counting from the object side.

WORKING EXAMPLE 1

In the following, Table 1 shows a specific numerical example of a zoomlens according to Working Example 1, which corresponds to Embodiment 1.In Table 1, r represents the curvature radius of the lens surfaces, drepresents the lens thickness or the air space between the lenses, nrepresents the refractive index of the lenses for the d-line, and vrepresents the Abbe number of the lenses for the d-line.

Table 2 shows the aspherical coefficients of the lens surfacesconstituting the aspherical surfaces. Each of the aspherical surfaceshas a rotationally symmetric aspherical surface shape represented by thefollowing equation:${SAG} = {\frac{H^{2}/R}{1 + \sqrt{1 - {\left( {1 + K} \right)\left( {H/R} \right)^{2}}}} + {D \cdot H^{4}} + {E \cdot H^{6}} + {F \cdot H^{8}} + {G \cdot H^{10}}}$where, SAG represents the amount of displacement of the lens surface atthe point apart from the optical axis by the height H in the radicaldirection with respect to the lens apex, R represents the curvatureradius, K represents the conical constant, and D, E, F and G representthe aspherical coefficient.

Table 3 shows the values of the variable air space at various zoomingpositions, when zooming is performed for a given object point located atinfinity, measured from the tip of the lens. In Table 3, the standardposition is a position where the zooming ratio of the second group isx−1, F/No and ω represent, respectively, the focal length, the F numberand the half angle of view of incidence at the wide-angle end, positionand the telephoto end of the zoom lens shown in Table 1. TABLE 1 groupsurface R D n ν 1  1 42.119 0.65 1.84666 23.9  2 17.684 3.10 1.6031160.7  3 −74.618 0.15  4 14.687 1.80 1.77250 49.6  5 40.000 var. 2  640.000 0.40 1.88300 40.9  7 4.338 1.98  8 −6.801 0.50 1.66547 55.2  95.300 1.80 1.84666 23.9 10 −43.097 var. 3 11 −10.000 0.55 1.69680 55.612 −80.000 0.27 13 14.355 1.65 1.60602 57.4 14 −15.716 var. 4 15 35.8901.95 1.48749 70.4 16 −9.660 0.45 1.84666 23.9 17 −30.874 0.12 18 14.5302.20 1.51450 63.1 19 −8.387 var. 5 20 ∞ 2.30 1.51633 64.1 21 ∞ 11.00 1.58913 61.2 22 ∞ —

TABLE 2 surface 8 13 14 18 19 K −2.17886E+00 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00 D −9.28339E−04 −2.51088E−04 1.17809E−04−1.95784E−04 4.38665E−04 E −7.18798E−07 −2.51467E−05 −2.54415E−05−1.46425E−05 −1.38232E−05 F −4.08791E−06 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00 G 9.18816E−08 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00

TABLE 3 wide-angle end standard telephoto end f 2.527 11.121 24.108 F/NO1.870 2.161 2.840 2ω 60.188 13.840 6.216 d5  0.500 9.774 12.650 d1016.600 7.326 4.450 d14 4.026 2.712 3.948 d19 1.000 2.313 1.078

FIGS. 2A to 4E show aberration charts of the zoom lens at the wide-angleend, the standard position and the telephoto end. FIGS. 2A, 3A and 4Aare the charts for the spherical aberration, with the solid lineindicating the values for the d-line. FIGS. 2B, 3B and 4B are the chartsfor the astigmatism, with the solid line indicating the sagittal fieldcurvature and the dotted line indicating the meridional field curvature.FIGS. 2C, 3C and 4C are the charts showing the distortion aberration.FIGS. 2D, 3D and 4D are the charts for the axial chromatic aberration,with the solid line indicating the values for the d-line, the dottedline indicating the values for the F-line and the dashed line indicatingthe values for the C-line. FIGS. 2E, 3E and 4E are the charts for thechromatic aberration of magnification, with the dotted line indicatingthe values for the F-line and the dashed line indicating the values forthe C-line.

As is evident from the aberration charts shown in FIGS. 2A to 4E, thezoom lens of Working Example 1 has an aberration correction capabilitysufficient to achieve high resolution.

The values for the conditional expressions in Working Example 1 are asfollows:|f3/f4|=4.04f3/fw|1=16.61|f3/BFw|=3.86|f31/f32|=1.30|nd31−nd32|=0.09|vd31−vd32|=1.8RIH=1.375φ41/RIH=0.01(φ41−φ43)/RIH=0.03

WORKING EXAMPLE 2

In the following, Table 4 shows a specific numerical example of a zoomlens according to Working Example 2, which corresponds to Embodiment 1.Table 5 shows the aspherical coefficients of the lens surfacesconstituting the aspherical surfaces. Table 6 shows the values of thevariable air space at various zooming positions, when zooming isperformed for a given object point located at infinity, measured fromthe tip of the lens. TABLE 4 group surface r d n ν 1  1 45.747 0.651.84666 23.9  2 18.436 3.10 1.60311 60.7  3 −60.132 0.15  4 14.023 1.801.77250 49.6  5 32.850 var. 2  6 32.850 0.40 1.88300 40.9  7 4.365 1.98 8 −6.556 0.50 1.66547 55.2  9 5.386 1.80 1.84666 23.9 10 −44.614 var. 311 −10.000 0.55 1.69680 55.6 12 −80.000 0.20 13 13.147 1.45 1.60602 57.414 −18.722 var. 4 15 27.257 2.00 1.48749 70.4 16 −9.718 0.45 1.8466623.9 17 −30.743 0.20 18 14.837 1.95 1.51450 63.1 19 −8.513 var. 5 20 ∞2.30 1.51633 64.1 21 ∞ 11.00  1.58913 61.2 22 ∞ −

TABLE 5 sur- face 8 13 18 19 K −3.86106E+00 0.00000E+00 0.00000E+000.00000E+00 D −1.88746E−03 −4.02222E−04 −1.90832E−04 4.51829E−04 E7.81554E−05 2.64132E−06 −3.03252E−06 −4.27485E−06 F −1.40338E−050.00000E+00 0.00000E+00 0.00000E+00 G 6.62510E−07 0.00000E+000.00000E+00 0.00000E+00

TABLE 6 wide-angle end standard telephoto end F 2.549 11.450 24.699 F/NO1.876 2.191 2.840 2ω 59.738 13.514 6.256 d5  0.500 9.838 12.650 d1016.600 7.262 1.315 d14 4.026 2.622 4.365 d19 1.000 2.404 1.091

FIGS. 5A to 7E show aberration charts of the zoom lens according toWorking Example 2 at the wide-angle end, the standard position and thetelephoto end.

As is evident from the aberration charts shown in FIGS. 5A to 7E, thezoom lens of Working Example 2 has an aberration correction capabilitysufficient to achieve high resolution.

The values for the conditional expressions in Working Example 2 are asfollows:|f3/f4|=4.74|f3/fw|=18.86|f3/BFw|=4.40|f31/f32|=1.27|nd31−nd32|=0.09|vd31−vd32|=1.8RIH=1.375φ41/RIH=0.013(φ41−φ43)/RIH=0.033

WORKING EXAMPLE 3

In the following, Table 7 shows a specific numerical example of a zoomlens according to Working Example 3, which corresponds to Embodiment 1.Table 8 shows the aspherical coefficients of the lens surfacesconstituting the aspherical surfaces. Table 9 shows the values of thevariable air space at various zooming positions, when zooming isperformed for a given object point located at infinity, measured fromthe tip of the lens. TABLE 7 group surface r d n ν 1  1 42.816 0.651.84666 23.9  2 17.686 3.10 1.60311 60.7  3 −75.026 0.15  4 14.570 1.801.77250 49.6  5 40.000 var. 2  6 40.000 0.40 1.88300 40.9  7 4.364 1.98 8 −6.818 0.50 1.66547 55.2  9 5.407 1.80 1.84666 23.9 10 −43.944 var. 311 −10.000 0.55 1.69680 55.6 12 −80.000 0.20 13 14.650 1.60 1.60602 57.414 −16.581 var. 4 15 22.551 1.80 1.48749 70.4 16 −9.718 0.45 1.8466623.9 17 −30.178 0.20 18 16.615 2.10 1.51450 63.1 19 −8.614 var. 5 20 ∞2.30 1.51633 64.1 21 ∞ 11.00  1.58913 61.2 22 ∞ −

TABLE 8 surface 8 13 14 18 19 K −3.72923E+00 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00 D −1.58644E−03 −6.95221E−04 −3.06071E−04−2.55430E−04 3.88552E−04 E 7.57996E−05 −8.74395E−06 −1.30855E−05−4.79720E−06 −6.72353E−06 F −1.53871E−05 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00 G 8.08638E−07 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00

TABLE 9 wide-angle end standard telephoto end f 2.539 11.248 24.817 F/NO1.878 2.191 2.850 2ω 59.964 13.738 6.214 d5  0.500 9.747 12.705 d1016.600 7.353 4.395 d14 4.026 2.656 4.026 d19 1.000 2.370 1.000

FIGS. 8A to 10E show aberration charts of the zoom lens according toWorking Example 3 at the wide-angle end, the standard position and thetelephoto end.

As is evident from the aberration charts shown in FIGS. 8A to 10E, thezoom lens of Working Example 3 has an aberration correction capabilitysufficient to achieve high resolution.

The values for the conditional expressions in Working Example 3 are asfollows:|f3/f4|=4.77|f3/fw|=19.21|f3/BFw|=4.47|f31/f32|=1.26|nd31−nd32|=0.09|vd31−vd32|=1.8RIH=1.375φ41/RIH=0.016(φ41−φ43)/RIH=0.036

EMBODIMENT 2

FIG. 11 shows the configuration of a small zoom lens according toEmbodiment 2 of the present invention.

The same structural components as those in FIG. 1 of Embodiment 1 aregiven the same reference numerals, and the description thereof has beenomitted.

Embodiment 2 is different from Embodiment 1 only in the configuration ofthe fourth lens group G4. The fourth lens group G4 of Embodiment 2 has apositive refractive power as a whole, and moves along the optical axissuch that the image plane, which is displaced by a movement of thesecond lens group G2 along the optical axis and by a movement of theobject, is maintained at a constant position with respect to a referenceplane. The fourth lens group G4 includes at least one asphericalsurface, and includes a lens 41 having a positive refractive power, alens 42 having a negative refractive power and a lens 43 having apositive refractive power, arranged in that order from the object side.In contrast to Embodiment 1, the lens 41 on the object side is a singlelens, and the lens 42 and the lens 43 that are on the image sideconstitute a cemented lens.

EXAMPLE 4

In the following, Table 10 shows a specific numerical example of a zoomlens according to Working Example 4, which corresponds to Embodiment 2.Table 11 shows the aspherical coefficients of the lens surfacesconstituting the aspherical surfaces. Table 12 shows the values of thevariable air space at various zooming positions, when zooming isperformed for a given object point located at infinity, measured fromthe tip of the lens. TABLE 10 group surface r d n ν 1  1 44.764 0.651.84666 23.9  2 18.093 3.10 1.60311 60.7  3 −68.829 0.15  4 14.829 1.801.77250 49.6  5 41.509 var. 2  6 41.509 0.40 1.88300 40.9  7 4.537 1.98 8 −6.603 0.50 1.66547 55.2  9 5.554 1.80 1.84666 23.9 10 −46.566 var. 311 −10.000 0.55 1.69680 55.6 12 −80.000 0.20 13 11.653 1.35 1.60602 57.414 −58.732 var. 4 15 12.681 1.70 1.51450 63.1 16 −14.391 0.35 17 ∞ 0.451.84666 23.9 18 14.867 2.25 1.48749 70.4 19 −7.554 var. 5 20 ∞ 2.301.51633 64.1 21 ∞ 11.00  1.58913 61.2 22 ∞ −

TABLE 11 sur- face 8 13 15 16 K −3.04317E+00 0.00000E+00 −5.07847E−01−3.10062E+00 D −1.38546E−03 −4.33897E−04 −2.80966E−06 7.34395E−04 E2.20637E−05 1.60648E−06 3.08781E−06 4.08252E−06 F −3.87080E−060.00000E+00 0.00000E+00 0.00000E+00 G 1.05179E−07 0.00000E+000.00000E+00 0.00000E+00

TABLE 12 wide-angle end standard telephoto end f 2.521 11.733 24.676F/NO 1.872 2.267 3.022 2ω 60.180 13.120 6.210 d5  0.500 9.767 12.720 d1016.600 7.333 4.380 d14 4.026 2.401 4.016 d19 1.000 2.625 1.009

FIGS. 12A to 14E show aberration charts of the zoom lens according toWorking Example 4 at the wide-angle end, the standard position and thetelephoto end.

As is evident from the aberration charts shown in FIGS. 12A to 14E, thezoom lens of Working Example 4 has an aberration correction capabilitysufficient to achieve high resolution.

The values for the conditional expressions in Working Example 4 are asfollows:|f3/f4|=28.16|f3/fw=105.08|f3/BFw|=24.32|f31/f32|=1.02|nd31−nd32|=0.09|vd31−vd32|=1.8RIH=1.375φ41/RIH=0.03(φ41−φ43)/RIH=0.056

EXAMPLE 5

In the following, Table 13 shows a specific numerical example of a zoomlens according to Working Example 5, which corresponds to Embodiment 2.Table 14 shows the aspherical coefficients of the lens surfacesconstituting the aspherical surfaces. Table 15 shows the values of thevariable air space at various zooming positions, when zooming isperformed for a given object point located at infinity, measured fromthe tip of the lens. TABLE 13 group surface r d n ν 1  1 34.170 0.651.84666 23.9  2 17.739 3.20 1.49700 81.6  3 −61.283 0.15  4 14.762 1.801.77250 49.6  5 43.687 var. 2  6 43.687 0.40 1.88300 40.9  7 4.471 1.98 8 −6.612 0.50 1.66547 55.2  9 5.560 1.80 1.84666 23.9 10 −41.180 var. 311 −10.000 0.55 1.69680 55.6 12 −80.000 0.20 13 12.663 1.35 1.60602 57.414 −40.439 var. 4 15 12.300 1.70 1.51450 63.1 16 −15.402 0.35 17 ∞ 0.451.84666 23.9 18 14.818 2.25 1.48749 70.4 19 −7.524 var. 5 20 ∞ 2.301.51633 64.1 21 ∞ 11.00  1.58913 61.2 22 ∞ −

TABLE 14 sur- face 8 13 15 16 K −3.57190E+00 0.00000E+00 −6.27182E−01−3.29444E+00 D −1.58537E−03 −3.73437E−04 −8.48880E−06 7.35383E−04 E2.82612E−05 −2.63365E−07 2.74820E−06 3.29235E−06 F −3.72365E−060.00000E+00 0.00000E+00 0.00000E+00 G 7.39995E−08 0.00000E+000.00000E+00 0.00000E+00

TABLE 15 wide-angle end standard telephoto end f 2.513 11.625 24.817F/NO 1.867 2.255 2.819 2ω 60.272 13.240 6.218 d5  0.500 9.775 12.736 d1016.600 7.325 4.365 d14 4.026 2.695 4.026 d19 1.000 2.331 1.000

FIGS. 15A to 17E show aberration charts of the zoom lens according toWorking Example 5 at the wide-angle end, the standard position and thetelephoto end.

As is evident from the aberration charts shown in FIGS. 15A to 17E, thezoom lens of Working Example 5 has an aberration correction capabilitysufficient to achieve high resolution.

The values for the conditional expressions in Working Example 5 are asfollows:|f3/f4|=23.99|f3/fw=90.53|f3/BFw|=20.86|f31/f32|=1.02|nd31−nd32|=0.09|vd31−vd32|=1.8RIH=1.375φ41/RIH=0.03(φ41−φ43)/RIH=0.055

EXAMPLE 6

In the following, Table 16 shows a specific numerical example of a zoomlens according to Working Example 6, which corresponds to Embodiment 2.Table 17 shows the aspherical coefficients of the lens surfacesconstituting the aspherical surfaces. Table 18 shows the values of thevariable air space at various zooming positions, when zooming isperformed for a given object point located at infinity, measured fromthe tip of the lens. TABLE 16 group surface r d n μ 1  1 47.499 0.651.84666 23.9  2 18.666 3.10 1.49700 81.6  3 −59.606 0.15  4 14.385 1.801.77250 49.6  5 36.141 var. 2  6 36.141 0.40 1.88300 40.9  7 4.643 1.98 8 −7.099 0.50 1.66547 55.2  9 −5.054 1.80 1.84666 23.9 10 −169.683 var.3 11 10.000 0.55 1.69680 55.6 12 −47.979 0.20 13 15.594 1.35 1.6060257.4 14 −50.058 var. 4 15 14.885 1.70 1.51450 63.1 16 −18.381 0.35 1721.291 0.45 1.84666 23.9 18 9.228 2.25 1.48749 70.4 19 −8.650 var. 5 20∞ 2.30 1.51633 64.1 21 ∞ 11.00  1.58913 61.2 22 ∞ −

TABLE 17 surface 8 13 14 15 16 K −2.62793E+00 0.00000E+00 0.00000E+004.71412E−01 8.46971E−01 D −1.18751E−03 −7.26655E−04 −3.29720E−049.66901E−06 6.52678E−04 E 2.51942E−05 −4.66447E−05 −4.37520E−054.09662E−06 5.12648E−06 F −5.50514E−06 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00 G 1.65637E−07 0.00000E+00 0.00000E+000.00000E+00 0.00000E+00

TABLE 18 wide-angle end standard telephoto end f 2.467 11.448 24.260F/NO 1.866 2.185 2.711 2ω 61.348 13.446 6.308 d5  0.500 9.714 12.736 d1016.600 7.386 4.395 d14 4.456 2.827 4.477 d19 1.000 2.599 0.949

FIGS. 18A to 20E show aberration charts of the zoom lens according toWorking Example 6 at the wide-angle end, the standard position and thetelephoto end.

As is evident from the aberration charts shown in FIGS. 18A to 20E, thezoom lens of Working Example 6 has an aberration correction capabilitysufficient to achieve high resolution.

The values for the conditional expressions in Working Example 6 are asfollows:|f3/f4|=54.7|f3/fw=200.31|f3/BFw|=50.368|f31/f32|=0.92|nd31−nd32|=0.09|vd31−vd32|=1.8RIH=1.375φ41/RIH=0.025(φ41−φ43)/RIH=0.046

EMBODIMENT 3

FIG. 21 is a diagram showing the configuration of a video cameraconstituted using the zoom lens of the present invention. Referencenumeral 211 denotes the zoom lens according to Embodiment 1, 212 denotesa low-pass filter, an IR absorbing glass and the like, 213 a to 213 cdenote color separation prisms, 214 a to 214 c denote CCDs, 215 denotesa signal processing circuit, and 216 denotes a viewfinder.

After unnecessary light components are removed with the low-pass filterand IR absorbing glass 212, light that has passed through the zoom lens211 is split into red, green and blue light with the color separationprisms 213 a to 213 c, then imaged on the light-receiving surfaces ofthe CCDs 214 a to 214 c. Output signals from the CCDs 214 a to 214 cthat correspond respectively to the red, green and blue light areoperated with the signal processing circuit 215, and a color image isdisplayed on the viewfinder 216. Furthermore, output signals from thesignal processing circuit 215 are input to a video recording circuit(not shown), and a video image is recorded in a particular recordingmedium.

Since the video camera according to this embodiment uses the zoom lensof the present invention, it is possible to provide a compact,high-image quality video camera.

It should be noted that the zoom lens of Embodiment 2 may be used as thezoom lens 211.

It is also possible to form a digital camera for recording still images,using a configuration similar to that shown in FIG. 21.

Each of the above-described embodiments is intended merely to clarifythe technical content of the present invention. The present invention isnot to be construed as limited to these specific examples, but to beconstrued in a broad sense, and may be practiced with variousmodifications within the sprit and the scope of the claims.

INDUSTRIAL APPLICABILITY

There is no particular limitation with respect to the application fieldsof the small zoom lens according to the present invention, and the zoomlens may be used, for example, for optical systems for use in ultrasmallthree-CCDs that are used for video cameras and the like.

1. A small zoom lens comprising: a first lens group that comprises alens having a negative refractive power, a lens having a positiverefractive power and a lens having a positive refractive power, arrangedin that order from an object side, that has a positive refractive poweras a whole, and that is fixed with respect to an image plane; a secondlens group that has a negative refractive power as a whole, and thatcauses a zooming action when moved along an optical axis; an aperturestop that is fixed with respect to the image plane; a third lens groupthat comprises a lens having a positive refractive power and a lenshaving a negative refractive power, that has a positive or negativerefractive power as a whole, and that is fixed with respect to adirection of the optical axis when zooming and when focusing; and afourth lens group that has a positive refractive power as a whole, andthat moves along the optical axis such that the image plane, which isdisplaced by a movement of the second lens group along the optical axisand by a movement of the object, is maintained at a constant positionwith respect to a reference plane.
 2. The small zoom lens according toclaim 1, wherein the second lens group comprises at least one asphericalsurface, and comprises a meniscus negative lens whose convex surfacefaces the object side, a lens having a negative refractive power and alens having a positive refractive power, arranged in that order from theobject side.
 3. The small zoom lens according to claim 1, wherein thethird lens group comprises at least one aspherical surface, andcomprises a meniscus negative lens whose concave surface faces theobject side and a lens having a positive refractive power, arranged inthat order from the object side.
 4. The small zoom lens according toclaim 1, wherein the third lens group satisfies the following Condition(1):4.01<|f3/f4|<60, where  (1) f3: focal length of the third lens group,f4: focal length of the fourth lens group.
 5. The small zoom lensaccording to claim 1, wherein the third lens group satisfies thefollowing Condition (2):14<|f3/fw|<210, where  (2) f3: focal length of the third lens group, fw:focal length of the entire system at the wide-angle end.
 6. The smallzoom lens according to claim 1, wherein the third lens group satisfiesthe following Condition (3):3<|f3/BFw|<55, where  (3) f3: focal length of the third lens group, BFw:back focus at the wide-angle end.
 7. The small zoom lens according toclaim 1, wherein the third lens group satisfies the following Condition(4):0.85<|f31/f32|<1.5, where  (4) f31: focal length of the first lens fromthe object side of the third lens group, f32: focal length of the secondlens from the object side of the third lens group.
 8. The small zoomlens according to claim 1, wherein the third lens group satisfies thefollowing Conditions (5) and (6):|nd31−nd32|<0.15  (5)|vd31−vd32|<3.0, where  (6) nd31: refractive index of the lens of thethird lens group that is on the object side, nd32: refractive index ofthe lens of the third lens group that is on the image side, vd31: Abbenumber of the lens of the third lens group that is on the object side,vd32: Abbe number of the lens of the third lens group that is on theimage side.
 9. The small zoom lens according to claim 1, wherein thefourth lens group comprises at least one aspherical surface and a pairof cemented lenses, and comprises a lens having a positive refractivepower, a lens having a negative refractive power and a lens having apositive refractive power, arranged in that order from the object side.10. The small zoom lens according to claim 1, wherein when a refractivepower of the surface of the fourth lens group that is closest to theobject side is φ41 and the maximum image height is RIH, the followingCondition (7) is satisfied:0.005<φ41/RIH<0.035.  (7)
 11. The small zoom lens according to claim 1,wherein a single lens is disposed closest to the object side in thefourth lens group, and when a refractive power of the surface of thesingle lens that is on the object side is φ41 and a refractive power ofthe surface of the single lens that is on the image side is φ42, thefollowing Condition (8) is satisfied:0.04<(φ41−φ42)/RIH<0.06.  (8)
 12. The small zoom lens according to claim1, wherein the fourth lens group comprises a cemented lens constitutedby a lens having a positive refractive power and a lens having anegative refractive power, and a single lens having a positiverefractive power, arranged in that order from the object side, and whena refractive power of the surface of the cemented lens that is closestto the object side is φ41 and a refractive power of the surface of thecemented lens that is closest to the image side is φ43, the followingCondition (9) is satisfied:0.025<(φ41−φ43)/RIH<0.045.  (9)
 13. A digital camera using the smallzoom lens according to claim
 1. 14. A video camera using the small zoomlens according to claim 1.